How can you simulate level of curiosity for a chat bot?
It's possible to implement a form of curiosity-driven behavior without requiring full 'emotional intelligence'. One elementary strategy would be to define some form of similarity measure on inputs.

More generally, Jurgen Schmidhuber has pioneered work on 'Artificial Curiosity/Creativity' and 'Intrinsic Motivation' and has written a number of papers on the subject:


Artificial Curiosity 
Intrinsic Motivation


Here is a video of a nice associated presentation.